An electric setting/operating device (actuator) for operating a rotary-type regulating valve, such as a butterfly valve, drives a valve stem coupled to an output shaft by transmitting a rotating force generated from a driving motor to the output shaft via a gear mechanism.
Such a setting/operating device generally has an emergency shutoff function that closes the regulating valve when the supply of electric power is stopped by interruption of electric service or the like. There is a known spring return type setting/operating device that closes a regulating valve by forcibly rotating an output shaft using a spring unit provided separately from the above gear mechanism as an electric setting/operating device having this emergency shutoff function.
A driving motor of the electric setting/operating device generally has a detent torque. Accordingly, when the supply of electric power to the setting/operating device is stopped, it is difficult to rotate the gear mechanism coupled to the driving motor from the output shaft side using the torque from the spring unit. Therefore, a general spring return type setting/operating device has a clutch mechanism for disconnecting the coupling between the driving motor and the gear mechanism. However, in spring return operation that drives the output shaft using a torque from the spring unit in the state in which the coupling to the driving motor is disconnected by the clutch mechanism, the rotation speed of the output shaft is higher than in motor operation that drives the output shaft using the rotating force of the driving motor. Accordingly, when the rotation of the output shaft is stopped by return operation, a large impact (referred to below as a “return impact”) is applied to gears included in the gear mechanism. Therefore, the conventional spring return type setting/operating device has a brake mechanism to reduce a return impact applied to gears, in addition to the clutch mechanism described above (see PTL 1 and PTL 2).